1. Field of Invention
The present invention relates to a combustion chamber in an internal combustion engine which permits the use of not only gas oil but also volatile fuel oils and low cetane number fuel oils. More particularly, it is concerned with a combustion chamber in an internal combustion engine in which engine starting performance and low load driving performance are improved.
2. Description of the Prior Art
A combustion chamber for the combustion of fuel oils, e.g. gas oil, is shown in a Diesel engine described in Japanese Utility Model Laid Open No. 150702/79. In this conventional combustion chamber structure, which is shown in FIG. 5 of the accompanying drawing, a main combustion chamber (c) in which there is inserted a fuel injection nozzle (b), and a subcombustion chamber (e) in which there is inserted an auxiliary firing device (d), communicate with each other and are formed in a piston (a), and a protuberant portion (f) is formed at the portion of communication between both combustion chambers (c) and (e).
In the above construction, the main and the subcombustion chamber communicate with each other in spite of the difficulty of disposing both the fuel injection nozzle and the auxiliary firing device in such a manner as to face the interior of a single combustion chamber. According to such a construction, there are attained freedom of layout and protection of the auxiliary firing device from heat load.
However, the above conventional construction involves the following drawbacks from the standpoint of combustibility.
The fuel injection nozzle used therein injects fuel into the main and subcombustion chambers independently of load and the number of revolutions, and it has a plurality of nozzle holes as shown in FIG. 5. Therefore, under the condition of low revolution and low load, including idling of the engine, the air-fuel mixture in the subcombustion chamber, which mainly functions to effect fire nucleation, becomes lean. As a result, the mixture is difficult to fire even when ignition is made by the auxiliary firing device. Further, there is a risk of misfire because of poor fire propagation.
The above problems result when gas oil is used as the fuel. In the case of the use of fuels of a low cetane number, namely, volatile fuel oils such as gasoline and alcohol, fuel oil injected into the subcombustion chamber is diffused into the main combustion chamber because of its thinness, resulting in the mixture in the subcombustion chamber becoming still leaner. One means for solving this problem may be throttling of intake air, but the resulting increase in pumping of the engine leads to the loss of output performance and deterioration of the fuel economy. Thus, this approach is not considered to be a good solution where it is desirable to develop a combustion chamber superior having combustion characteristics.